So i am at the end of the game, and as the scrub that I am, I missed out on 4 agents.
-Jana whom I let join the Warden (ended up being killed)
-Magister Alexius (I sent to work for redcliff mages, not research because i didnt have arcane perk >.<)
-Blades of Hessarian (I didn't know that I could recruit them and considering how they killed my troops, i slaughtered those bastards. Turns out they can be nice.....)
-Clemence (Dude is easily miss-able in the beginning...)
I'm going to be up front. My ADHD, OCD or whatever is killing me. I need closure on this matter. Should I re-roll? Do these agents matter slightly? This run was going to be my canon run because it is my first. I was going to make this the play through that goes through future dlc and such but the fact that i missed some things is killing me. If I make another play through and get everything. it's not the same because of different characters. The void would not be filled. Sooooooo re roll? MAssive REROLL?????!#@? Some one please convince me and my issues that missing these guys is not important. please...............
I got three of those. I sided with templars so I got Ser Barris instead of Alexius.
If you aren't willing to stand by your choices, then you should re-roll the playthrough from the first save, since some of those characters are pretty important. Don't make your first playthrough your canon one unless you meta-game, which means playing ahead or reading ahead to see the consequences, or unless you are willing to accept any mistakes.
I didn't know about the Blades either, but I hadn't gotten that far past them when I discovered it, so I reloaded. The Blades are pretty important. They help keep the area safe from the darks and reds later on.
Jana gets murdered if you don't recruit her. So you should.
Clemence just helps Cullen and isn't that important. But story-wise it is good to bring in a tranquil because it shows you are compassionate.
I don't think Alexius has any special effect on the game, but I think making him an agent provides an approval boost from Dorian.
However, if you don't want to re-roll your playthrough then you can always make the Alexius change in the Dragon Age Keep. None of the other characters show up in keep at the moment.